Crystal Bar released the statement: “We are working very closely with the police regarding the allegation. Thus far, police have raised no criticism of the day to day operation of the premises.

“We are mindful of the concerns our customers may have regarding this allegation, and in view of this we will review our security procedures before the forthcoming weekend.”

At present, CCTV footage of Carver Street and Crystal Bar has been unsuccessful in finding the attacker. South Yorkshire Police are urging anybody with information of people acting suspiciously to come forward.

Detective constable Jon Kirkham stated: “Since police received the allegation, we have been working closely with the victim and the nightclub to collect as much information as we can about what happened that evening. This had included meticulously reviewing CCTV footage from inside and outside Crystal, in an attempt to piece together the victim’s movements and also identify any suspicious activity.

“The victim is receiving support from officers and at this time is unable to provide any further information about who may have been responsible for this incident.

“We now need the public’s help to gather information about any suspicious activity they may have witnessed in Crystal that night, between 12.45am and 1.45am on Sunday 7 May. I’d also be keen to hear from anyone who saw anything suspicious in the surrounding area at similar times.

If you have information or have witnessed anything, contact South Yorkshire Police on 101 with the incident number 179.